Instructions on Sheet Pile Construction

Instructions on Sheet Pile Driving

In construction, to reduce the water impact against steel sheet piles, first should drive piles starting from the upstream and inside of river, then pile the river downstream and outside. In piling, use construction techniques combined with press and drive way.

When need to prolong steel sheet piles by welding, must use same type, same strength. In welding, firstly butt welding or seam-weld interlockings, then weld sheet piles. Joints of the adjacent steel sheet piles must be dislocated more than 6m and shall not exceed 50% in the same plane.

Instructions on Purlin and Support Installation

Cofferdam is the sheet pile walls that form into a circle. For safe and stable sheet pile project , usually it requires steel purlin and inside steel support. Producing and processing of purlin and inside support should be combined by the situation in plant and construction site. And should be uniform and in accordance with universal standard. When items or parts made by factory transported to the construction scene, must be assembled as a whole at the site in order to ensure accurate structure and size.

Processing of steel purlin parts must be finalized to complete on the model pedestal .

Basic methods to install purlin is to use steel casing with concrete piles to support pole beams, use pole beams, jacks and mandrel hanger system to layered lift and decentralize purlin and finally fix it to the casing.

Permeability Proof and Anti-Leakage Treatments

A. In all processes of steel sheet pile driving, must use guide and oriented device, strictly control the vertical degree at both sides to make interlockings connected very closely between piles. Because assurance of sheet pile’s vertical degree and be close around the purlin are the key points to avoid permeability and leakage.

B. In pit’s pumping, for leakage from loose interlockings, use cotton with rich fiber to plug and block.

C. For wide slit between piles, use flax roots mixed with butter to stuff and seal the seam to aovid permeability and leakage, or use fly ash, saw wood foam and expansive cement to scatter along the pile surface in the flow direction outside the cofferdam.

Technology Notes on Smooth Sheet Pile Construction

In sheet pile project, usually we need to set guide device, pump water, install support and weld piles. In order to ensure smooth construction process, there are some important notices.

Notes on Sheet Pile Welding

Elevation of supports’ faces must be consistent, each node should be welded by the node map, strengthen the connection, welding rods shall meet the construction specifications.

Steel support, spliced by welding, must use way of tear welding by regulations, like should fully weld the seam, at welding seam surface, welding wave is required uniform, not allow any pores, slag, cracks, sarcoma and so on. The quality of welding and inspection system should be strictly enforced.

Setting Guide or Oriented Device

Use two section steels as oriented control clamp, place and fix it in position. In case of shock must re-adjust to fix. In the driving of steel sheet pile, generally we need to send pile to the required elevation first, at this time, should remove the fixture first then gradually lift pile.

Setting oriented devices is to ensure the right sheet pile axis after construction, oriented pile or guide beam could be replaced by profile steel or wood, the spacing between the beams is just the width of sheet pile walls. In order to maintain accurate distance, between the beams, we can embed a temporary skids at certain intervals. After use, oriented devices can be removed for next section’s use.

Notes on Pumping

In steel sheet pile cofferdam, not pump until strength of concrete back cover is more than 90%. When the water level pumped inside the cofferdam is 0.5m below the steel support, stop pumping until support’s installation is completed. When pumping, pay  attention to the force status between steel sheet pile and support.

Notes on Support Installation

Welded purlin as a whole should be at the same line from upper to lower part in order to enhance the overall stability of the support system. Before steel support’s installation,  pull through the twine first and mark the midline on the purlin.

Steel support and steel sheet piles should against each other very tightly, between each bars connections should be pretty solid, in the construction process of bearing platform, should always check force conditions between pile and support.

Article Source : sheet pile manufacturer, supplier - shunli sheet piling industrial co.,Ltd

Why Need Guide Device in Sheet Pile Wall Construction

Setting guide or oriented devices is to ensure the right sheet pile axis after construction, oriented pile or guide beam could be replaced by profile steel or wood, the spacing between the beams is just the width of sheet pile walls. In order to maintain accurate distance, between the beams, we can embed a temporary skids at certain intervals. After use, guide or oriented devices can be removed for next section’s use.

How to set ?

Use two section steels as oriented control clamp, place and fix it in position. In case of shock must re-adjust to fix it. In the driving of steel sheet pile, generally we need to send pile to the required elevation first, at this time, should remove the fixture first then gradually lift the pile.

How to Check Sheet Pile Deformation

Use inclinometer to measure sheet pile. 

Take steel sheet pile for example, firstly weld a φ75mm steel pipe in the groove of steel sheet pile and pile the pipe together with steel sheet pile. Insert inclinometer to the tube fixed with sand filled in. 

Although inclinometer can measure the horizontal displacement, it means little to distinguish safety of steel sheet pile, because the cofferdam allow a great amount of displacement (up to 100 ~ 300 mm). 

What means alot here is the sheet pile bending measurement, which could be obtained by numerical differentiation of curvature from inclinometer data. This is the reliable results to determine whether the steel sheet pile meet deformation requirements. It can also be used to compare with the moment from calculation results to indirectly get stiffness information of sheet pile wall.

How to Check Sheet Pile Before Construction

Firstly,  after the arrival of sheet piles, check whether the model is consistent as design, if not, re-calculate the strength and support of sheet pile.

Secondly, when go into the construction site, all sheet piles are required for inspection first, only a complete and straight sheet pile can be brought into the scene. For used-piles (like steel sheet pile), particularly should emphasis on inspection.  Because used sheet piles in Pile, transportation and stacking process are easily deformed by external factors. If do not check, some may not easy to pile or drive.

Inspection method

Use a little flat car with a 1.5 ~ 2.0m long standard sheet pile put on, check sheet piles going along with the standard pile from start to finish. Once a defect is discovered adjust it asap.

After this checking, when in the transport and stacking, make sure not bend them, avoid the collision, in particular, do not break the continuous lockings. Stack space should be flat and solid not producing a large settlement. At the bottom of sheet pile stack, should pad wood blocks. Piles with different sections should be separated in different stacks, between each stacks should set aside certain channels to facilitate the moving for crane or transport vehicle.

Sheet Pile Design in One of Beijing-Shanghai High-Speed Railway Projects

Based on the hydrological and geological conditions around the main bridge of Jinan Yellow River Bridge of Beijing-Shanghai High-Speed Railway Project in China, for sheet pile cofferdam design and construction, we introduced the thinking of design, comparison of two sheet pile design proposals and reasons for selection.

Project Description

The length of Jinan Yellow River Bridge, one of sections of Beijing-Shanghai High-Speed Railway project,  is 5.143km. The main bridge is 112+3*168+112m supported by continuous steel with same height. A  stiffened arch was set in the middle, height of truss is 16m and width 30m, distance between sections is 14.0m. The main piers are No. 0 ~ 5, in which No.1,2,3 and 4 Pier all use 28 pieces of Φ2.5m bored piles, the bearing platform is 6.0m in thickness and 42.5m*23.3m in plane size. While No.0 and 5 Pier use 21 pieces of Φ2.0m bored piles, bearing platform is 4.5m in thickness and size 34.6m*13.8m. Concrete of bearing platform is C45 type.

Bearing platforms of No.1 and 2 pier of main bridge are in the main river cap (year-round water), others are in the south shallow beach area. Elevation of top surface of pier No.0 pier is +33 m (ground elevation is +33.50 m), No.1 pier +27 m, No.2 Pier +27 m, No.3 +27 m (ground elevation +30.14 m), No.4 +27 m (ground elevation +29.91 m), No.5 +30 m (ground elevation +30.92 m).

Thinking of Design

 

According to detailed information on geological exploration, No.3,4 and 5 Pier Yellow River main bridge is located in the floodplain south of Yellow River, silt and silt layers are rich in water within 19m below the ground surface, and there is a a hard plastic-like clay layer 2m below (elevation is about +9 ~ + 11 m) with relative complete and uniform distribution. The main bridge’s No. 1 and 2 pier is located in main channel of Yellow River, the riverbed’s elevation is + 17 ~ 24 m, the surface is covered by loose silt,  between +9 ~ +11 m there is a 2m thick layer of hard plastic-like clay. And this layer is confirmed in the piling or driving construction of steel casing and bored pile, the soil samples removed are sticky and large hard plastic-like clay block. So based on detailed construction surveys, the bearing platform of main Bridge’s No.1,2,3 and 4 Pier will use steel sheet pile cofferdam program. For No.0 and 5 pier, because of shallow excavation depth, method of open-excavation and protection in porcess will be used.

 

Comparison and Selection

 

Option One : Long Steel Sheet Pile Program

The flat surface of steel sheet pile cofferdam is rectangular for the base of the main bridge, the inner mouth size is 46.5m*28.3m, steel sheet pile is 24m each.

Mouth elevation at the end of steel sheet pile cofferdam for No.1 and 2 pier in water is 7.0m, top elevation 31m (top elevation of bearing platform add 27 m, flood elevation is +30.5 m), Mouth elevation at the end of steel sheet pile cofferdam for No.3 and 4 pier at beach is +6.5 m, the top surface elevation +30.5 m.

Use German Larsen IV (or shunli cold formed type) steel sheet pile . The cofferdam is made by single layer steel sheet pile, 3 layers of steel tubes and inside steel support formed by beams. Inside ring-support (purlin) for steel sheet piles use I56 compsite structure and internal support use 630mm steel pipe.

For sheet pile wall construction on land, pile by hydraulic vibratory hammer with the help of 50t crawler crane; for sheet pile wall construction in water, use 40t gantry crawler crane for water platform and hydraulic vibratory hammer.

For excavation and soil clear inside cofferdam on land,  use long arm excavation machine and high-pressure water jetting for soil suction method; for the ones in water, use method of high-pressure water jetting for dredging. Considering  the end of steel sheet pile will be piled or drove into the hard plastic-like clay layer between +9 ~ +11 m deep, after soil clear or dredging, sheet pile wall or cofferdam could not do bottom sealing, instead directly drain the water inside the cofferdam, and then pour 20 cm thick concrete pads, then remove steel casing, chisel trailer coupling and start construction of bearing platform.

Advantages : No bottom sealing reduces the risk of concrete construction in large area and construction investment, reduces the dredging depth of the cofferdam and saves lot of sealing concrete. At the same time, within the cofferdam, excavation, dredging, construction of concrete pads are all in dry place, improves the efficiency and speed up the construction schedule.

Disadvantages : Length of steel sheet pile added 6m increases the cost in itself.

Option two : Short Sheet Pile Program

Use 18m long steel sheet pile, the others are same as Option One. Considering the steel sheet pile cofferdam is in relative loose silt layer, bottom sealing in water will be carried out after soil clear within cofferdam, then until strength of the sealing concrete meet requirements drain the water, and then remove the steel casing, chisel pile head, and start construction of bearing platfrom.

Advantages : Length of steel sheet pile reduced 6 m will lower investment in itself.

Disadvantages : Because of bottom concrete sealing in water, it increases the construction difficulty of excavation in water and dredging within the cofferdam, reduces construction efficiency. And bottom concrete sealing construction in large area and generous amount would bring high risk and difficulty, a lot of extra sealing concrete also increases the uncertainty and costs on construction.

 

Program Selection

 

Through repeated investigations on site and programs’ comparison, option one is determined to use. From the construction technology, safety and reliability considerations, if by option one,  though water can not be drained inside the cofferdam, can also continue with Option two, there is not much risk. Also from an economic point of view, construction cost of the option one is much lower than Option two, the successful implementation would mean significant cost savings.

Sheet Pile Cofferdam Design with 6 Layers of Inside Support

Construction process of sheet pile cofferdam with six-layer inside support is generally divided into six steps of pumping and excavation down and five steps of concrete pouring and support demolition. The most dangerous condition is excavation to the end. For design, key points are as follows:

1. First set the guide frame of sheet pile, insert and play, then install the first layer purlin and support (to avoid high tide). Then try pumping water and plug pile joints in water over the riverbed. 

 
2. From layer 2 to 6, pump or excavate one by one to the position 0.5m lower than the elevation of support to be installed, then install purlin and support.

 
3. From the 5th layer, gradually narrow the excavation surface layer to form slope. 

 
4. Excavate by divided area to the end of cushion, pouring concrete pads, and ultimately form a complete flat construction surface. 

 
5. Pouring cap by four-layer, backfill sands from nearby and remove a support layer as soon as each layer’s pouring completed. 

 
6. For the last 2 layers’ support, should consider the construction situation for support removal or change when pouring the upper parts of bridge piers.

In addition, in the calculation and design, select datas of drilling holes in the place with poor geological conditions. Then refer to section diagram, analyze and calculate the displacement and bending moment of sheet pile in the six steps’ pumping and excavation.

Sheet Pile Wall Structure Designs on Seriously Weathered Rock Layer

For sheet pile wall or cofferdam construction, normally we need to drive piles to the required depth. But for shallow layer especially seriously weathered rock layer, it is very difficult to drive piles. For instance, top surface of highly weathered rock and sand layer is 1-4m lower than cushion base, and some part is even near the cushion base. Because the driving depth is not enough as required, the displacement at the pile-end will be larger, sheet piles in some project sections would easily get damaged like "kicking damage".

For this problem, we must take some measures on structural design first.

For structral desgin of sheet pile wall, there are mainly three plans to solve the problem :

1. Enlarge the wall or cofferdam and put slope inside;

2. Increase inside support layers;

3. Reinforce the bottom of sheet piles;

Sheet Pile Wall or Cofferdam

Comparing three plans above, if only by plan 1, because the wall or cofferdam is normally large enough, it will cost extra money or time. And if there are more wall or cofferdams in construction at the same time, it will influence other projects too; Just by plan 2, if we increase inside support layers when excavation near the end, supports' changing process will be more complicated when it comes to the back concrete cover; If just by plan 3, although it is applicable in theory, it is not enough for pratical construction.

The best way actually is to combine the strong points of the three plans. For instance, firstly, we can set the axis line of sheet pile wall near the cap side which will proive a certain slope space and is useful for sheet pile reinforcement.Secondly, set 6 layers of inside support,make the space wider at the upper 4 layers. At last, at the location higher than layer elevation of 7.0m, set steel tubular pile (or called steel pipe pile) as support foot right near the driving-hole of sheet piles.

Sheet Pile Repair and Reinforcement

At present in the world methods of sheet pile repair and reinforcement mainly include two categories : Local Repair and Reinforcement Method and Set Alternative Retaining Structure Method.

Local Repair and Reinforcement Method includes : Steel Repair and Weld Method, local Outside Cover Reinforcing Method, Lower Beam Cover Elevation Method and Improve Soil Properties behind the Wall Method;

For Method of Setting the Alternative Retaining Structure includes : Add Underground Continuous Wall Method and Add Alternative Steel Sheet Pile Method.

Which Method to Use

Due to technical conditions, the actual project cases of steel sheet pile structure repair and reinforcement are very few.  For research, we suggest use ANSYS software to build simulation models for structure reinforced, compare deformation, internal force and stress produced by all reinforcement methods to discuss and analyse the technical feasibility and reliability of these repair and reinforcement methods.

Why Need Sheet Pile Reinforcement and Repair

With strong capacity, watertight and simple to use and good durability etc., sheet pile of steel become the mainstream materials in modern construction industry.In the harbor or port's shore structure which used to connects wharf structure and slope as sheet pile retaining,steel sheet pile itself is vulnerable to erosion and damage. So we need to repair and reinforce sheet piles.